AS & A Level Chemistry - 9701 Paper 4 2019 Summer Zone 1

(a) Aqueous solutions of copper(II) salts contain the blue-coloured [Cu(H2O)6]2+ complex ion. Separate portions of this blue solution react with aqueous sodium hydroxide and with concentrated hydrochloric acid.

Give the following information for each of these reactions.

● reaction with aqueous sodium hydroxide
ionic equation .......................................................................................................................................
type of reaction ..................................................................................................................................
colour and state of the copper-containing product .............................................................

● reaction with concentrated hydrochloric acid
ionic equation .......................................................................................................................................
type of reaction ..................................................................................................................................
colour and state of the copper-containing product .............................................................
[6]

(b) Chloride ions can be identified using aqueous silver nitrate, AgNO3(aq).

$$\text{Ag}^+(\text{aq}) + \text{Cl}^-(\text{aq}) \rightarrow \text{AgCl}(\text{s})$$

0.303 g of a chloride of sulfur is completely hydrolysed with water. All the chlorine atoms present in the chloride of sulfur are converted into chloride ions. The solution is diluted to 100.0 cm^3. A 25.00 cm^3 sample of this solution is titrated with 0.0500 mol dm^{-3} AgNO3(aq). The titration requires 22.40 cm^3 of 0.0500 mol dm^{-3} AgNO3(aq).

Calculate the empirical formula of the chloride of sulfur. Show all your working.

empirical formula of chloride of sulfur = .............................. [3]

(a) Group 2 nitrates decompose when heated.

Write an equation for the decomposition of strontium nitrate.

(b) Describe and explain how the thermal stability of Group 2 nitrates changes with increasing atomic number.

(c) The variation in the thermal stability of Group 2 amides is similar to that of Group 2 nitrates.

(i) Suggest whether calcium amide, $\text{Ca(NH}_2\text{)}_2$, will decompose more or less readily than barium amide, $\text{Ba(NH}_2\text{)}_2$. Explain your answer.

(ii) $\text{Ba(NH}_2\text{)}_2$ decomposes when heated to form barium nitride, $\text{Ba}_3\text{N}_2$, and ammonia as the only products.

Write an equation for this reaction.

(d) $\text{Ba(NH}_2\text{)}_2$ contains the $\text{NH}_2^-$ ion.

Predict the bond angle of $\text{NH}_2^-$. Explain your answer using the qualitative model of electron-pair repulsion. 

Chlorate(V) ions are powerful oxidising agents.
(a) The reduction of chlorate(V) ions, $ClO_3^-$, with $SO_2$ forms chlorine dioxide, $ClO_2$, and sulfate ions, $SO_4^{2-}$, as the only products.
Construct an equation for this reaction.
.................................................................................................................. [1]
(b) (i) Chlorine dioxide, $ClO_2$, disproportionates with hydroxide ions, $OH^-$ (aq), to form a mixture of $ClO_2^-$ and $ClO_3^-$ ions.
$$2ClO_2 + 2OH^- \rightarrow ClO_2^- + ClO_3^- + H_2O$$
Explain, using this reaction as an example, what is meant by disproportionation.
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(ii) Deduce the ionic half-equations for the reaction in (b)(i).
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(c) A lithium-iodine electrochemical cell can be used to generate electricity for a heart pacemaker. The cell consists of a lithium electrode and an inert electrode immersed in body fluids. When current flows lithium is oxidised and iodine is reduced.
(i) Use the Data Booklet to write half-equations for the reactions taking place at the two electrodes. Hence write the overall equation for when a current flows.
• ..................................................................................................................
• ..................................................................................................................
overall equation ............................................................................................ [2]
(ii) Use the Data Booklet to calculate the $E_{cell}^\circ$ for this cell.
$E_{cell}^\circ = $ .......................... V [1]
(iii) A current of $2.5 \times 10^{-5}$ A is drawn from this cell.
Calculate the time taken for 0.10 g of lithium electrode to be used up. Assume the current remains constant throughout this period.
time = .......................... s [3]

(a) Sketches of the shapes of some atomic orbitals are shown.
Identify the type of orbital, s, p, or d.

[1]

(b) Cadmium forms the two ions, Cd$_2^+$ and Cd$^{2+}$. The electronic configuration of cadmium in these ions is shown.
- [Kr] 4d¹⁰5s¹
- [Kr] 4d¹⁰
Use this information to explain why cadmium is not a transition element.
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[1]

(c) Methylamine, CH$_3$NH$_2$, is a monodentate ligand.
(i) State what is meant by the term monodentate in this context.
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[1]
In the presence of aqueous methylamine, [Cd(H$_2$O)$_6$]$^{2+}$ reacts to form a mixture of two isomeric octahedral complexes.
equilibrium 1
[Cd(H$_2$O)$_6$]$^{2+}$ + 4CH$_3$NH$_2$ ⇌ [Cd(CH$_3$NH$_2$)$_4$(H$_2$O)$_2$]$^{2+}$ + 4H$_2$O
ΔH^θ = -57 kJ mol^-1
(ii) Complete the three-dimensional diagrams to show the isomers of [Cd(CH$_3$NH$_2$)$_4$(H$_2$O)$_2$]$^{2+}$.
Use L to represent CH$_3$NH$_2$ in your diagrams.

[2]

(d) (i) State what is meant by the term stability constant.
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[1]
(ii) Complete the table by placing one tick (✔) in each row to suggest how increasing temperature will affect K_stab and the equilibrium concentration of the cadmium complex, [[Cd(CH$_3$NH$_2$)$_4$(H$_2$O)$_2$]$^{2+}$], for equilibrium 1. Explain your answer.
[Table_1]
explanation ..................................................................................................
.............................................................................................................
[2]
EDTA^4- is a polydentate ligand. When a solution of EDTA^4- is added to [Cd(H$_2$O)$_6$]$^{2+}$ a new complex [CdEDTA]$^{2-}$ is formed.
The values for the stability constants for two Cd$^{2+}$ complexes are shown.
[Table_2]
(iii) A solution containing equal numbers of moles of CH$_3$NH$_2$ and EDTA is added to [Cd(H$_2$O)$_6$]$^{2+}$.
Predict which complex is formed in the larger amount. Explain your answer.
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[1]

(e) Methylamine is a Brønsted-Lowry base.
Write an equation showing how methylamine dissolves in water to give an alkaline solution.
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[1]

(f) Methylamine is a useful reagent in organic chemistry.
(i) Write an equation for the reaction of ethanoyl chloride with methylamine.
..............................................................................................................
[2]
(ii) Methylamine also reacts with propanone to form compound P as shown.

Deduce the type of reaction shown here.
..............................................................................................................
[1]

(a) Chlorate(I) ions undergo the following reaction under aqueous conditions.
$$2NH_3 + ClO^- \rightarrow N_2H_4 + Cl^- + H_2O$$
A series of experiments was carried out at different concentrations of $ClO^-$ and $NH_3$.
The table shows the results obtained.

[Table_1]

| experiment | [ClO^-] / mol dm^-3 | [NH₃] / mol dm^-3 | initial rate / mol dm^-3 s^-1 |
|------------|-----------------------------|------------------------------|----------------------------------|
| 1 | 0.200 | 0.100 | 0.256 |
| 2 | 0.400 | 0.200 | 2.05 |
| 3 | 0.400 | 0.400 | 8.20 |

(i) Use the data in the table to determine the order with respect to each reactant, $ClO^-$ and $NH_3$.
Show your reasoning.
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[2]

(ii) Write the rate equation for this reaction.
rate = .........................................................................................................................
[1]

(iii) Use the results of experiment 1 to calculate the rate constant, $k$, for this reaction. Include the units of $k$.
$k = ext{..........................}$
units = ext{.......................}$
[2]

(iv) On the axes sketch a graph to show how the value of $k$ changes as temperature is increased.



[1]

(b) In another experiment, the reaction between chlorate(I) ions and iodide ions in aqueous alkali was investigated.
A solution of iodide ions in aqueous alkali was added to a large excess of chlorate(I) ions and $[I^-]$ was measured at regular intervals.
(i) Describe how the results of this experiment can be used to confirm that the reaction is first-order with respect to $[I^-]$.
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[2]

A three-step mechanism for this reaction is shown.
Step 1: $ClO^- + H_2O \rightarrow HClO + OH^- $
Step 2: $I^- + HClO \rightarrow HIO + Cl^-$
Step 3: $HIO + OH^- \rightarrow H_2O + IO^- $

(ii) Use this mechanism to deduce the overall equation for this reaction.
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[1]

(iii) Identify a step that involves a redox reaction. Explain your answer.
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[1]

(a) Complete the table by placing one tick (✔) in each row to indicate the sign of each type of energy change under standard conditions.

[Table_1]


[1]

(b) Explain what is meant by the term enthalpy change of atomisation.

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[1]

(c) The overall reaction for the atomisation of liquid bromine molecules, $Br_2(l)$, is shown.

$$Br_2(l) \rightarrow 2Br(g)$$

This happens via a two-step process.

• Construct a labelled energy cycle to represent this atomisation process, including state symbols.
• Use your cycle and relevant data from the Data Booklet to calculate the enthalpy change of vaporisation of $Br_2(l)$, $\Delta H_{vap}^{\circ}$:
The enthalpy change of atomisation of bromine, $\Delta H_{at}^{\circ}$ = +112 kJ mol$^{-1}$.

$$\Delta H_{vap}^{\circ} = \text{........................} \text{kJ mol}^{-1}$$ [3]

(d) Suggest how the $\Delta H_{vap}^{\circ}$ of iodine, $I_2(l)$, would compare to that of bromine, $Br_2(l)$. Explain your answer.

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[1]

(e) (i) Explain what is meant by the term enthalpy change of hydration.

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[1]

(ii) Suggest why the enthalpy change of hydration of $Br^-(g)$ is more exothermic than that of $I^-(g)$.

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[2]

(a) Benzene can be converted into cyclohexane.

(i) For this reaction name the type of reaction and identify the reagent and conditions needed.
type of reaction ..............................................................
reagent and conditions ...................................................
[2]
(ii) State the bond angles in benzene and cyclohexane.
bond angle in benzene .............................. bond angle in cyclohexane ..............................
Explain your answers.
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[2]

(b) When benzene reacts with $SO_3$, benzenesulfonic acid is produced.

The mechanism of this reaction is similar to that of the nitration of benzene. Concentrated $H_2SO_4$ is used in an initial step to generate the $SO_3H^+$ electrophile as shown.
$$SO_3 + H_2SO_4 \rightarrow SO_3H^+ + HSO_4^-$$
(i) Draw a mechanism for the reaction of benzene with $SO_3H^+$ ions. Include all necessary curly arrows and charges.

[3]
(ii) Write an equation to show how the $H_2SO_4$ catalyst is reformed.
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[1]

(c) 3-dodecylbenzenesulfonic acid can be prepared from benzenesulfonic acid.

Suggest the reagents and conditions and name the mechanism for this reaction.
reagents and conditions ...................................................
mechanism ..........................................................
[2]

(d) When concentrated sulfuric acid is added to water, dissociation takes place in two stages.
stage 1 $H_2SO_4 \rightleftharpoons H^+ + HSO_4^-$
stage 2 $HSO_4^- \rightleftharpoons H^+ + SO_4^{2-}$ $K_{a2} = 1.0 \times 10^{-2} \text{mol dm}^{-3}$
$K_{a2}$ is the acid dissociation constant for stage 2.
(i) Write the expression for the acid dissociation constant $K_{a2}$.
$K_{a2} =$ .................................................................
[1]
(ii) $H_2SO_4$ is considered a strong acid whereas $HSO_4^-$ is considered a weak acid.
Suggest how the magnitude of the acid dissociation constant for stage 1 compares to $K_{a2}$.
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[1]

(e) Benzoic acid, $C_6H_5CO_2H$, is a weak acid. A solution of $0.0250 \text{mol dm}^{-3}$ benzoic acid has a pH of 2.90.
Calculate the $K_a$ of benzoic acid.

$K_a = ............................... \text{mol dm}^{-3}$
[2]

(a) The mass spectrum of compound $X$, $C_5H_{10}O_2$, is recorded.
The peak heights of the M and M+1 peaks are 22.65 and 1.25 respectively.
(i) Use these data to show that there are five carbon atoms present in one molecule of $X$.
Show your working.
[1]
(ii) The mass spectrum has a peak at $m/e = 57$.
Complete the equation to show the fragmentation of $X$ to produce this peak.
$[C_5H_{10}O_2]^+ \to \text{..............................} + \text{..............................}$
[2]

(b) State the use of TMS and $CDCl_3$ in NMR spectroscopy.
• TMS .....................................................
• $CDCl_3$ ...............................................

(c) The proton NMR spectrum of compound $X$, $C_5H_{10}O_2$, is shown.

(i) By considering both the relative peak areas and their $\delta$ values, use the Data Booklet to
• deduce the part of the molecule that produces the peak at $\delta$ 2.2,
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• deduce the part of the molecule that produces the peaks at $\delta$ 1.2 and $\delta$ 3.5,
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• deduce the part of the molecule that produces the peak at $\delta$ 4.0.
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[3]
(ii) When reacted with aqueous alkaline iodine, $X$ produces a yellow precipitate.
Use this information and your answers to (c)(i) to suggest a structure for $X$.
[1]

(d) Compound $W$ is an ester with the molecular formula $C_5H_{10}O_2$.
The proton NMR spectrum of $W$ contains only two peaks.
The relative areas of these two peaks are in the ratio $9 : 1$.
Suggest a structure for this ester, $W$.
[1]

(e) Compound $V$ is a carboxylic acid which contains a chiral centre. It also has the molecular formula $C_5H_{10}O_2$.
(i) Explain what is meant by the term chiral centre.
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[1]
(ii) Suggest a structure for $V$.
[1]

(a) Organochlorine compounds can undergo hydrolysis.

$\text{R–Cl} + \text{H}_2\text{O} \rightarrow \text{R–OH} + \text{HCl}$

State and explain the relative rates of hydrolysis of the following compounds.

CH$_3$CH$_2$Cl CH$_3$COCl C$_6$H$_5$Cl
................................................................................................................................. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. .................................................................................................................................
[3]

(b) Epibatidine is a naturally occurring organochlorine compound.


(i) Epibatidine is a weak base.
State what is meant by the term weak base.
................................................................................................................................. .................................................................................................................................
[1]

A molecule of epibatidine contains two nitrogen atoms, both of which can act as a base.
(ii) Epibatidine reacts with HCl(aq).
Complete the structure to suggest the product formed in this reaction.

[1]

(c) Polyamides, such as nylon-6, can be prepared from a monomer that contains both an amine and an acyl chloride functional group.


(i) When the nylon-6 monomer is hydrolysed, bonds are broken and formed.
By considering the two steps in the mechanism of the reaction, complete the table by placing one tick (✓) in each row to indicate the types of bonds broken and formed during the mechanism.

[Table_1]
σ bonds only π bonds only both σ and π bonds
bonds broken
bonds formed
[1]
(ii) Draw two repeat units of nylon-6. The amide bond should be shown fully displayed.
................................................................................................................................. [2]

(d) An addition polymer made from two different alkene monomers is called a co-polymer. A section of a polyalkene co-polymer is shown.

Draw the structure of the two alkene monomers which produce this co-polymer.
[2]

(e) Explain why polyamides normally biodegrade more readily than polyalkenes.
................................................................................................................................. ................................................................................................................................. [1]

(f) The alkene phenylethene can be prepared from benzene in three steps.

(i) Deduce the identity of compound H and draw its structure in the box.
[1]
(ii) Suggest reagents and conditions for each of the steps 1–3.
step 1 .................................................................................................................................
step 2 .................................................................................................................................
step 3 .................................................................................................................................
[3]